1. Field of the Invention
The present disclosure relates to a liquid crystal display device and a method of fabricating the same, and more particularly, to a liquid crystal display device having enhanced transmittance and a method of fabricating the same.
2. Discussion of the Related Art
In general, a liquid crystal display device has characteristics such as light weight, thin profile, low power consumption, and the like, and the application area thereof has been gradually expanded due to such characteristics. Accordingly, liquid crystal display devices are widely used as a means for displaying a screen in a portable computer, a portable phone, office automation equipment, or the like.
Typically, the liquid crystal display device displays desired images on a screen thereof by controlling an amount of the optical transmission based on image signals applied to a plurality of control switching elements arranged in a matrix form.
The liquid crystal display device is configured by including a liquid crystal panel in which a color filter substrate that is an upper substrate and a thin-film transistor array substrate that is a lower substrate are disposed to face to each other and a liquid crystal layer is formed between the two substrates, and a driving unit for operating the liquid crystal panel by supplying scan signals and image information to the liquid crystal panel.
The liquid crystal display devices having such a configuration are divided into a vertical electric field application type and a horizontal electric field application type according to the direction of an electric field driving the liquid crystals.
The vertical electric field application type liquid crystal device includes a thin-film transistor array substrate and a color filter substrate facing to each other in which a plurality of pixels are defined, a liquid crystal layer formed between the thin-film transistor array substrate and the color filter substrate, a pixel electrode formed for each pixel that is defined on the thin-film transistor array substrate, and a common electrode formed on the color filter substrate, and therefore, the vertical electric field application type liquid crystal device having such a configuration drives liquid crystals in the liquid crystal layer by vertical electric field formed between the pixel electrode and the common electrode. As an example, there are a twisted nematic (TN) mode liquid crystal display device and an electrically controlled birefringence mode liquid crystal display device.
The horizontal electric field application type liquid crystal device includes a thin-film transistor array substrate and a color filter substrate facing to each other in which a plurality of pixels are defined, a liquid crystal layer formed between the thin-film transistor array substrate and the color filter substrate, and a plurality of pixel electrodes and common electrodes alternatively formed substantially in parallel for each pixel that is defined on the thin-film transistor array substrate, and therefore, the horizontal electric field application type liquid crystal device having such a configuration drives liquid crystals in the liquid crystal layer by horizontal electric field formed between the pixel electrode and the common electrode. As an example, there is an in-plane switching (IPS) mode liquid crystal display device.
Among such various liquid crystal display devices, the IPS mode liquid crystal display device has an advantage of wide viewing angle due to a small birefringence change to the direction of viewing angle, and in recent years, the trend of employing the IPS mode liquid crystal display device continues to increase.
However, the advantage of wide viewing angle in the IPS mode liquid crystal display device also creates an adverse effect such as a danger of violating the user's privacy by neighboring persons close to a liquid crystal display device in use when using a computer for his or her personal purposes, leaking confidential information when carrying out his or her duties including confidential matters, or the like.
In order to solve such confidential problems, a liquid crystal display device has been proposed in which a viewing angle control sub-pixel for selectively implementing an ECB mode or an off mode is further provided in addition to red, green, and blue sub-pixels.
Hereinafter, a liquid crystal display device having such a viewing angle control sub-pixel will be described in brief with reference to FIG. 1.
As illustrated in FIG. 1, a liquid crystal display device in the related art is configured by including a first substrate 1 and a second substrate (not shown); a gate line 2 and a data line 3 formed to intersect vertically and horizontally with each other on the first substrate 1 for defining red, green, and blue pixels and a viewing angle control pixel; a backlight shielding pattern (BLSP) 5 formed at a circumference of the red, green, and blue pixels and the viewing angle control pixel; a thin-film transistor 4 having a gate electrode 4a, a source electrode 4b, and a drain electrode 4c, which is formed at each region intersected by the gate line 2 and the data line 3 on the first substrate 1; a plurality of first pixel electrodes 6 and first common electrodes 10 alternatively formed to be apart from each other by a predetermined distance at the red, green, and blue pixels on the first substrate 1; a second pixel electrode 7 formed at the viewing angle control pixel on the first substrate 1; and a second common electrode (not shown) formed to correspond to the second pixel electrode 7 on the second substrate.
Furthermore, a gate insulation film (not shown) is formed on the gate line 2, the gate electrode 4a of the thin-film transistor 4, and the backlight shielding pattern 5, a protective film (not shown) is formed on the data line 3, and the source electrode 4b and drain electrode 4c of the thin-film transistor 4, and a first contact hole 11 and a second contact hole 13 for exposing part of the drain electrode 4c of the thin-film transistor 4 and the backlight shielding pattern 5, respectively, which are formed at the red, green, and blue pixels and the viewing angle control pixel, are formed on the gate insulation film and protective film, wherein the drain electrode 4c of the thin-film transistor 4 is connected to the first pixel electrode 6 through the first contact hole 11 for the red, green, and blue pixels, the drain electrode 4c of the thin-film transistor 4 is connected to the second pixel electrode 7 by the first contact hole 11 for the viewing angle control pixel, and the backlight shielding pattern 5 of the red, green, and blue pixels is connected to the first common electrode 10 by the second contact hole 13. Furthermore, all the backlight shielding patterns 5 formed at the red, green, and blue pixels and the viewing angle control pixel are connected to one another to form an integrated body.
The liquid crystal display device having such a configuration in the related art may be driven by selecting a narrow viewing angle mode or a wide viewing angle mode.
More specifically, when driven in the wide viewing angle mode, the red, green, and blue pixels are driven, but the viewing angle control pixel is not driven, thereby forming horizontal electric fields between the first pixel electrodes 6 and the first common electrodes 10 in the liquid crystal layer corresponding to the red, green, and blue pixels. In this manner, it may be similarly driven as an IPS mode liquid crystal display device when the red, green, and blue pixels are driven but the viewing angle control pixel is not driven, thereby implementing a wide viewing angle.
In addition, when driven in the narrow viewing angle mode, the red, green, and blue pixels and the viewing angle control pixel are all driven, thereby forming horizontal electric fields between the first pixel electrodes 6 and the first common electrodes 10 in the liquid crystal layer corresponding to the red, green, and blue pixels, and forming vertical electric fields between the second pixel electrodes 7 and the second common electrodes (not shown) in the liquid crystal layer of the viewing angle control pixels. As a result, light is leaked in the direction of an inclined (lateral) viewing angle, thereby implementing a narrow viewing angle in which viewing of a screen cannot be facilitated.
Nevertheless, a liquid crystal display device according to the related art, as described above, has a disadvantage of low transmittance because the number of viewing angle control pixels, which are used only for controlling a viewing angle but not used for displaying colors, occupies a quarter of the total number of pixels, and therefore, studies for enhancing the transmittance thereof are actively carried out. In particular, according to the liquid crystal display device in the related art, as described above, electric fields are not formed on part or all of the first pixel electrodes 6 and the first common electrodes 10 of the red, green, and blue pixels, thereby causing a main reason for reducing the transmittance thereof. Moreover, according to the liquid crystal display device in the related art, as described above, two contact holes (first and second contact holes) should be necessarily formed for each of the red, green, and blue pixels, and one contact hole (second contact hole) should be necessarily formed for each viewing angle control pixel, thereby causing a reason for reducing the transmittance thereof because of the area occupied by the contact holes within a pixel.